1. Field of the Invention
The present invention relates to a braking force control system of a vehicle which adequately distributes the braking force in braking.
2. Description of the Related Art
In recent years, there have been proposed various braking control systems which make use of constitutions of anti-lock braking systems (ABS) and control distribution of braking force in normal braking to be more adequate one.
For example, in JP-A-10-119744, there is disclosed one which independently increases, decreases or holds braking oil pressure of each of right and left rear wheels when deceleration of a vehicle reaches a specified value and when a vehicle speed exceeds a specified speed, so that braking force distribution between rear and front wheels becomes an approximately ideal one to perform independent braking control for carrying out sufficient braking.
Incidentally, in the ABS control and the braking force distribution control as described above which provide an independent braking for the rear wheel side, because of not so large transfer of a vertical load between the right side and left side wheels in a normal turning of the vehicle, an attitude of the vehicle does not change largely in rolling even when the brake is operated, so that the braking can be performed with a normal feeling of the rolling. However, in a high lateral acceleration turn on a high friction road, when the ABS control and braking force distribution control of the rear wheels are independently carried out, because of a large difference between the right and left vertical loads, there is a fear that unpleasant rolling behavior of the vehicle body is occurred due to change in breaking force of the turning outside rear wheel caused by each of the braking controls.
The present invention was made in view of the above with an object of providing a braking force control system of a vehicle which can carry out natural, reliable and stable braking without any particular addition of complicated mechanisms by preventing the occurrence of unpleasant rolling behavior. When a vehicle turns with a high lateral acceleration, the braking of each of the right and left rear wheels is independently controlled.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a braking force control system of a vehicle, having: a lateral acceleration detecting unit detecting lateral acceleration of the vehicle; and a braking control unit carrying out an anti-lock braking control and carrying out an independent braking control of right and left rear wheels, wherein, in a case that the lateral acceleration exceeds a lateral acceleration value set beforehand, when the anti-lock braking control is operated at one of the right and left rear wheels, the braking control unit executes a stepwise pressure increase control for providing a stepwise pressure increase for the other rear wheel up to a braking pressure to be reached at a start of the control.
Namely, in the above-described braking force control system of a vehicle according to the first aspect of the invention, the lateral acceleration detecting unit detects lateral acceleration of the vehicle. Moreover, the braking control unit executes, when the lateral acceleration exceeds a lateral acceleration value set beforehand, stepwise pressure increase control which provides, when the anti-lock braking control is operated at one of the right and left rear wheels, a stepwise pressure increase for the other rear wheel up to a braking pressure to be reached at a start of the control. Therefore, at a high lateral acceleration turning, at a turning outside rear wheel for which operation of an anti-lock braking control is slowed due to an increase in a vertical load, a stepwise pressure increase control is started from the time of operation of the anti-lock braking control at a turning inside rear wheel. Thus, even the anti-lock braking control is operated at the turning outside rear wheel, no sudden strong braking is applied and unpleasant rolling behavior is prevented from occurrence to allow a natural, reliable, and stable braking to be performed. In addition, this can be applied by changing control of normal anti-lock braking control, so that the realization thereof is allowed without any particular addition of complicated mechanism.
Further, according to a second aspect of the present invention, there is provided a braking force control system of a vehicle, having: a lateral acceleration detecting unit detecting a lateral acceleration of the vehicle; and a braking control unit carrying out an anti-lock braking control and carrying out an independent braking control of right and left rear wheels, wherein the braking control unit executes a braking force distribution control between front and rear wheels as specified when the lateral acceleration exceeds a lateral acceleration value set beforehand, and when the anti-lock braking control is operated at one of the right and left rear wheels, the braking control unit stops the front and rear braking force distribution control of the other rear wheel and executes a stepwise pressure increase control thereof for providing a stepwise pressure increase up to a braking pressure to be reached at a start of the control.
Namely, in the above-described braking force control system of a vehicle as the second aspect, the lateral acceleration detecting unit detects lateral acceleration of the vehicle. Moreover, the braking control unit executes, when the lateral acceleration exceeds a lateral acceleration value set beforehand, braking force distribution control between front and rear wheels as specified, and along with this, when the above anti-lock braking control is operated at one of the right and left rear wheels, stops the front and rear braking force distribution control of the other rear wheel and executes stepwise pressure increase control thereof which provides a stepwise pressure increase up to a braking pressure to be reached at a start of the control. Therefore, at high lateral acceleration, the front and rear braking force distribution control is first carried out at the turning inside rear wheel with subsequently started anti-lock braking control. Also in the turning outside rear wheel, the front and rear braking force distribution control is started subsequent to the turning inside rear wheel. However, when the anti-lock braking control is started at the turning inside rear wheel in the course of the front and rear braking force distribution control, the front and rear braking force distribution control is stopped for the stepwise pressure increase control being executed. In this way, at the turning inside rear wheel, after the front and rear braking force distribution control, the control is transferred to the anti-lock braking control. While, at the turning outside rear wheel, after the front and rear braking force distribution control, the control is transferred to the anti-lock braking control through the stepwise pressure increase control. Thus, even the anti-lock braking control is operated at the turning outside rear wheel, no sudden strong braking is applied and unpleasant rolling behavior is prevented from occurrence to allow a natural, reliable, and stable braking to be performed. In addition, this can be applied by changing control of normal anti-lock braking control, so that the realization thereof is allowed without any particular addition of complicated mechanism.
Furthermore, in the braking force control system of a vehicle according to the second aspect of the present invention, the front and rear braking force distribution control is started and executed depending on a slipping condition of the rear wheel.